Magnetic bearings are used in different rotating machines such as electric motors, compressor, turbines or the like in order to maintain the axial or/and radial positions of a rotating shaft by means of magnetic fields acting on a rotor of the machine.
Axial magnetic bearings are often used to reject axial disturbances coming from the industrial environment (pressure waves and oscillations) that can create unwanted effects on the behaviour of the rotor of the turbine or the compressor such that limit cycles, vibrations, instabilities.
The axial bearing force is built using a pair of electromagnets connected to power amplifiers (classically one power amplifier per electromagnet) for which the control voltage is adapted by a controller. However, the unlaminated nature (an unlaminated bearing contributes to the eddy currents creation) of the thrust magnetic bearing limits the controller action. The dynamic of the actuator is considerably reduced (an axial bearing cannot reject disturbances located outside of a specific bandwidth frequencies) and the iron losses are increased.
So, as a known solution, when it is possible, the axial bearing design is changed (introduction of slots or use of a laminated design) to break or at least limit the eddy current creation and to reduce losses. Other solutions based on using specific material, for example insert made of ferromagnetic powder, are also identified.
However, all of those known solutions cannot be generalized because they are expensive and increase the magnetic bearing cost. Moreover, they cannot be used for each bearing due to mechanical limitations such as reduction of the mechanical resistance or reduction of the available force for example.